1. Technical Field
The invention relates to control of power takeoff operation equipment installed on a hybrid-vehicle and more particularly to back up, twelve-volt, direct current supported power takeoff operation of the equipment.
2. Description of the Problem
The use of a hybrid-vehicle chassis to support power takeoff operation (PTO) of equipment such as an aerial lift unit (colloquially called a “cherry picker”), a compactor on a garbage truck, a liquid fuel delivery pump on a tanker truck and the like, is relatively new, even in the context of the development of hybrid-vehicles. Integration of the control of PTO equipment on the hybrid-vehicle poses specific challenges.
It is favored practice to use hybrid-vehicle electric traction motors to support PTO as opposed to using the vehicle's internal combustion (IC) engine. A reason for this is that the vehicle's IC engine, typically a diesel capable of moving the vehicle at highway speeds, is designed to provide far more power than is required by the PTO equipment and accordingly is not operated in an optimal manner when the vehicle is supporting PTO operation. The problem is magnified in the environment of an aerial tower vehicle where the vehicle is not moving during PTO operation and PTO operation may only be occasional as and when demanded by an operator. If the IC engine is kept running to be ready for PTO, much fuel is wasted with the engine idling while waiting for operator inputs and in parasitic losses at the low power output levels. Electric motors by contrast suffer far less from parasitic losses than do thermal engines and demand relatively little power input in excess of their output. Moreover, electric motors are not run at idle. Use of the primary traction motor to power a high-pressure high-volume hydraulic pump allows greater efficiency over use of an idling diesel engine to power a PTO hydraulic pump.
For some types of PTO, particularly aerial lift units, it is necessary to provide a backup prime mover. In an aerial lift unit a small output direct current electric motor driving an auxiliary hydraulic pump is advantageously used. The DC electric motor can run off the twelve volt direct current source such vehicles are conventionally equipped with instead of the much higher voltage traction system. Thus the back up motor is supplied with electricity from a different source than the traction motor uses to energize the primary pump. An automotive starter motor may be used as the backup motor, such motors being relatively inexpensive.
However, the potential for conflict exists between the PTO hydraulic pump driven by the traction motor and the emergency hydraulic pump powered by the twelve volt DC motor. Such conflict may result in damage to the emergency hydraulic pump or its DC motor, which have a much lower maximum power output than do the primary PTO pump and motor.
Many contemporary vehicles are now equipped with body computers, local controllers and controller area networks to implement most aspects of vehicle control. In vehicles designed, built and sold by International Truck and Engine Corporation, an Electrical System Controller (“ESC”) carries out the functions of the body computer. Local controllers which communicate with each other and with the ESC to distribute data and requests essential for operation of local programming by which control is implemented. Controller area networks have been applied both to conventional vehicles and to hybrid-vehicles. Control strategies relating both to the primary and backup motors are preferably implemented on the ESC, which will control the operation of both motors.